Internal seal for the piston of a rotary engine

ABSTRACT

The invention relates to an internal seal for the piston of a rotary engine of trochoid type having a housing with two end parts and with a shell having a multi-arcuate interior surface. The piston is in the housing and is rotatably mounted on an eccentric. The said internal seal has an axially movable scraper ring held in spring contact with the adjacent end wall of the housing. The function of the scraper ring is to prevent passage of coolant or lubricant from the piston into the working chambers.

United States Patent [1 1 Schmadeke et al.

[ 1 Mar.4, 1975 INTERNAL SEAL FOR THE PISTON OF A ROTARY ENGINE [76]Inventors: Wolfgang Schmadeke,

Cacilienstrabe 29, Heilbronn; Gottlieb Wilmers, Friedhofstrabe 25,Neuenstadt, both of Germany [22] Filed: Apr. 2, 1973 [21] Appl. No.:346,761

3,191,945 6/1965 Andresen...... 277/88 3,194,569 7/1965 Utvitch....277/88 3,291,493 12/1966 Blair 277/92 3,400,939 9/1968 Jones 418/1423,535,061 10/1970 Yamamoto 418/142 3,540,815 11/1970 Belzner et a1418/142 FOREIGN PATENTS OR APPLICATIONS 1,016,540 1/1966 Great Britain418/142 Primary Examiner-John .1. Vrablik Attorney, Agent, or FirmKane,Dalsimer, Kane, Sullivan and Kurucz [57] ABSTRACT The invention relatesto an internal seal for the piston of a rotary engine of trochoid typehaving a housing with two end parts and with a shell having amultiarcuate interior surface. The piston is in the housing and isrotatably mounted on an eccentric. The said internal seal has an axiallymovable scraper ring held in spring contact with the adjacent end wallof the housing. The function of the scraper ring is to prevent passageof coolant or lubricant from the piston into the working chambers.

8 Claims, 5 Drawing Figures f/f l INTERNAL SEAL FOR THE PISTON OF AROTARY ENGINE BACKGROUND OF THE INVENTION In the known internal sealsfor pistons of a rotary engine, the juncture between the scraper ringand the piston is sealed by means of an elastic O-ring exerting a radialforce. Since this O-ring must be installed with a certain amount ofprestress, it opposes resistance to axial motions of the scraper ringrelative to the piston. This resistance must be overcome by acorrespondingly strong contact spring to achieve positive contact of thescraper ring with the adjacent end wall of the housing. This results inincreased wear, both at the stripping edge of the scraper ring and onthe end wall of the housing. Furthermore, as a result of thermal andmechanical stress, the O-ring may suffer permanent deformation and theinternal seal may leak.

To ensure at least an easy axial displaceability of the scraper ring, ithas been proposed that the O-ring be arranged axially behind the scraperring. In this arrangement, however, the O-ring remains in direct contactwith the piston, which becomes relatively hot in operation, so that thelife of the elastic O-ring is limited. Besides, in this arrangement theO-ring is stressed exclusively in compression, with resulting very smallspring displacements, given the contact pressure required.

SUMMARY OF THE INVENTION The object of the invention is to provide animproved internal seal for a piston of a rotary engine which permitsrelatively easy axial mobility of the scraper ring and secondly prolongsthe service life of the rubber-like elastic seal between the scraperring and the piston.

This object is achieved by the instant invention by fixedly uniting thescraper ring to a coaxial supporting ring by means of a rubber-likeelastic ring stressed predominantly in shear.

Thus, the scraper ring is displaceable in axial direction withoutfriction, except for internal friction in the rubber-like elastic ring.Under these circumstances, the prestress when the internal seal isinstalled in the piston may be very small. Inasmuch as the rubber-likeelastic ring is separated from the hot piston by the supporting ring,the thermal stress on the elastic ring is substantially reduced. Springdisplacements of adequate length are obtainable because the elastic ringis stressed predominantly in shear. The internal seal, consisting of thescraper ring, the elastic ring and the supporting ring, may be set intoan annular recess in one face of the piston with the supporting ringbeing preferably located radially inwardly, having a press fit on theinner periphery of the annular recess. If the internal seal is to be setinto a circular recess in one wall of the piston, the supporting ringmay form the radially inner flange ofa ring of U-shaped cross sectionembracing the scraper ring, its radially outer flange making a press fitin the circular recess in the piston wall.

In another embodiment ofthe invention, the supporting ring likewiseforms a scraper ring axially movable in an annular recess in one face ofthe piston or in a separate holder ring attached to the end wall of thepiston.

The scraper ring may take the form of a segment of thin-walled tubing,the part of which projects axially from the supporting ring, beingbeveled radially outward to form a stripping edge. A scraper ring ofthis type may be produced at low cost by bending a strip of suitablematerial into a ring and butt-welding it at the joint.

According to this invention, positive sealing between the piston andscraper ring is assured even though the elasticity of the rubber-likematerial should decrease with time. In order to attain adequate contactpressure of the scraper ring with the adjacent housing wall in suchcase, an additional metal contact spring may be provided for the scraperring; this ring may be comparatively small, since as aforementioned, therubber-like elastic ring only insignificantly impedes free axialmobility of the scraper ring.

BRIEF DESCRIPTION OF FIGURES Embodiments of the invention will now bedescribed, by way of example, with reference to the drawings.

FIG. 1 shows a sectional view of one embodiment of an internal seal setinto an annular recess in the face of the piston.

FIG. 2 shows a sectional view of a second embodiment of an internal sealset into a circular recess in the end wall of the piston.

FIG. 3 shows a sectional view of a third embodiment of an internal sealagain set in an annular recess in the wall of the piston, the supportingring taking the form of a scraper ring as well.

FIG. 4 is a fragmentary sectional view of the engine with the housingshell and one housing end part, the eccentric shaft and the eccentricwith a further embodiment ofinternal seal set in the manual recess inthe wall of the piston.

FIG. 5 is a plan view of the scraper ring made of metallic material bentinto a ring and butt welded at the joint in accordance with a furtherrefinement of the present invention.

gether with the wall 3 of the adjacent end part 4 of the housing definesan annular space 5 which is sealed off from space 5a, containinglubricant or coolant, by an internal seal generally designated 6. Theinternal seal 6 is set into an annular recess 7 in the piston wall I andconsists of a scraper ring 8 with beveled stripping edge 9, fixedlyunited by a rubber-like elastic ring 10 to a coaxial supporting ring 11arranged inside the scraper ring 8. The rubberlike elastic ring 10 isjoined to the scraper ring 8 and supporting ring 11 preferably byvulcanizing. The supporting ring 11 has a press fit on the innerperiphery 12 of annular recess 7.

The elastic ring 10 in the first instance forms an absolutely tight sealbetween the scraper ring 8 and the piston wall 1, and moreover providesthe necessary axial contact pressurefor the scraper ring 8. Upon axialmotion of scraper ring 8 relative to supporting ring 11, the elasticring 10 is stressed practically exclusively in shear, permittingcomparatively great spring displacements with adequate contact pressure.The heat effect on the elastic ring 10 is comparatively light, since thesupporting ring 11 separates it from the hot piston.

In the embodiment of FIG. 2, the supporting ring 11 forms the radiallyinner flange of a holder ring 13 of U- shaped cross-section, itsradially outer flange l4 making a press fit in a circular recess 15 inthe piston wall 1. The scraper ring 8' in this case consists of asegment of thin-walled tubing, its face 16 projecting from holder ring13 being beveled radially outwardly to form a stripping edge. Thescraper ring 8 is again fixedly united to flange 11' by a rubber-likeelastic ring stressed practically exclusively in shear when scraper ring8' moves axially. In this embodiment, the holder ring 13 is bathed bythe piston coolant, so that the rubber-like elastic ring 10 is notsubjected to any appreciable heat load.

The scraper ring 8 may be made of metallic material bent into a ring andbutt-welded at the joint as shown in FIG. 5. The scraper ring may thenbe made especially small and light possessing a high natural frequency,which favors tight contact of scraper ring 8' with the adjacent housingwall 3.

In order to avoid adequate contact pressure of scraper ring 8 in theevent of diminished elasticity of the rubber-like ring 10, an additionalcontact spring 17 may be employed. In this embodiment, the spring is inthe form of a dish spring with apertures 1.7a to lessen its rigidity.

In the embodiment of FIG. 3, the scraper ring 8 and rubber-like elasticring 10 are essentially similar in form to the embodiment of FIG. 1. Thesupporting ring 11'' in this case, however, is in the form of an axiallymovable scraper ring having a beveled stripping edge. This ring is setinto recess 7 together with the elastic ring 10 and the scraper ring 8.The unit consisting of rings 8, 10 and 11" is pressed axially againstthe adjacent housing wall 3 by a corrugated spring 18. The rubber-likeelastic ring 10 then need follow only relatively slight axial motions ofscraper ring 8. In this embodiment, the seal between supporting ring 11"and piston wall 1 is provided by a metallic sealing ring 19 of C- shapedcross section. In a modification of the embodiment of FIG. 3 shown inFIG. 4, the unit consisting of rings 8, 10 and 11" may be arranged in aholder ring [13' of U-shaped cross section, set, like the holder ring 13in FIG. 2, into a circular recess in the piston walls. The springs 18and 19 will then cooperate with the corresponding walls of the holderring.

We claim:

1. An internal seal for the piston ofa rotary piston engine of trochoidtype having a housing with two end parts and with a shell, havingmulti-arcuate interior surface, in which housing the piston is rotatablymounted on an eccentric, said internal seal having an axially movablescraper ring held in spring contact with the adjacent end wall of thehousing, a coaxial supporting ring, a rubber-like elastic ring beingadapted to be separated from the piston by the supporting ring, thescraper ring fixedly united to the coaxial supporting ring by therubberlike elastic ring which is stressed predominantly in shear whenthe scraper ring moves axially relative to the supporting ring, thescraper ring, the elastic ring and the supporting ring being fixedlyunited and undetachably interconnected to form and function as a singleunit.

2. An internal seal according to claim 1 wherein the supporting ringforms the radially inner flange of a holder ring of U-shaped crosssection embracing the scraper ring, the holder ring having a radiallyouter flange capable of being set into an end wall of the piston.

3. An internal seal according to claim 1 wherein the supporting ring isin the form of a scraper ring capable of being set axially movable in anannular recess in a piston wall.

4. An internal seal according to claim 1 wherein an additional contactspring is provided for the scraper ring.

5. An internal seal according to claim 1 wherein the supporting ring isin the form of a scraper ring capable of being set axially movable in aseparate holder ring attached to the piston wall.

6. An internal seal according to claim 1, wherein the supporting ring isin the form of a scraper ring, and the unit consisting of the scraperring, the elastic ring and the supporting ring is set axially movable ina separate U-shaped holder ring attached to the piston wall, and furthercomprising a contact spring between the end of the supporting ringopposite to its scraper edge and the adjacent wall of the holder ring.

7. An internal seal according to claim 1 wherein the scraper ring is inthe shape of a segment of thin-walled tubing with a face thereofprojecting from the supporting ring and being beveled radially outwardlyto form a stripping edge.

8. An internal seal according to claim 7 wherein the scraper ring isformed ofa strip of metal bent into a ring and butt-welded at the joint.

UNITED STATES PATENT QEETEE CERTIFICATE OF CORREQTWW PATENT NO. 13,869,230 DATED March 4, 1975 INVENTOR(5) WOLFGANG SCHMADEKE andGOTTLIEB WILMERS It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

The name of the assignees should be inserted:

--=Audi NSU Auto Union Aktiengesellschaft, Neckarsulm/Wurttemberg,

West Germany and WANKEL GmbH Lindau/Bodensee, West Germany.,

Signed and gealed this A ttes t."

RUTH C. MASON C. MARSHALL DANN Arresting Officer

1. An internal seal for the piston of a rotary piston engine of trochoidtype having a housing with two end parts and with a shell, havingmulti-arcuate interior surface, in which housing the piston is rotatablymounted on an eccentric, said internal seal having an axially movablescraper ring held in spring contact with the adjacent end wall of thehousing, a coaxial supporting ring, a rubber-like elastic ring beingadapted to be separated from the piston by the supporting ring, thescraper ring fixedly united to the coaxial supporting ring by therubberlike elastic ring which is stressed predominantly in shear whenthe scraper ring moves axially relative to the supporting ring, thescraper ring, the elastic ring and the supporting ring being fixedlyunited and undetachably interconnected to form and function as a singleunit.
 2. An internal seal according to claim 1 wherein the supportingring forms the radially inner flange of a holder ring of U-shaped crosssection embracing the scraper ring, the holder ring having a radiallyouter flange capable of being set into an end wall of the piston.
 3. Aninternal seal according to claim 1 wherein the supporting ring is in theform of a scraper ring capable of being set axially movable in anannular recess in a piston wall.
 4. An internal seal according to claim1 wherein an additional contact spring is provided for the scraper ring.5. An internal seal according to claim 1 wherein the supporting ring isin the form of a scraper ring capable of being set axially movable in aseparate holder ring attached to the piston wall.
 6. An internal sealaccording to claim 1, wherein the supporting ring is in the form of ascraper ring, and the unit consisting of the scraper ring, the elasticring and the suPporting ring is set axially movable in a separateU-shaped holder ring attached to the piston wall, and further comprisinga contact spring between the end of the supporting ring opposite to itsscraper edge and the adjacent wall of the holder ring.
 7. An internalseal according to claim 1 wherein the scraper ring is in the shape of asegment of thin-walled tubing with a face thereof projecting from thesupporting ring and being beveled radially outwardly to form a strippingedge.
 8. An internal seal according to claim 7 wherein the scraper ringis formed of a strip of metal bent into a ring and butt-welded at thejoint.